1. Field of the Invention
The present invention relates to a filter for the elimination of radio noise. More particularly, the present invention relates to a filter comprising several wound capacitors having a common electrode layer.
2. Description of the Prior Art
As is known, class Y type filters comprise at least two capacitors, which can be connected between respective phases of the electrical power supply and ground, for the elimination of asymmetrical noise. In addition, it is common practice to equip such filters with at least one capacitor, forming a class X type filter, which can be connected between the phases of the electrical power supply for the elimination of symmetrical noise. Ultimately, the filters of the type mentioned above can be implemented in such a way as to obtain capacitive circuits of various configurations, depending on the specific requirements.
There is a known implementation of such filters with a single winding comprising a continuous metal sheet and a discontinuous metal sheet separated by a dielectric tape. A certain number of single capacitors (for example, three) are thus obtained so as to have a first common wound electrode layer consisting of the continuous metal sheet and a second wound electrode layer consisting of respective portions of a discontinuous metal sheet.
Due to electrical insulation reasons, the dielectric tape is wider than the metal sheets. The metal sheets are connected in a known fashion to contact terminals, of the blade (vane) type, coming out axially of the front side of the wound layer. Preferably, only the portions of the discontinuous metal sheet are equipped with terminals, for the respective connections to the ground and to the phases of the power supply system.
The single-winding capacitive filters of this type are easy and compact to build. However, they present stray inductances due to the fact that the continuous metal sheet has a relatively high number of turns.
Such stray inductances are formed due to the common wound layer of the three capacitors and negatively affect the operation of the entire capacitive filter; in fact, the filter operation may be unacceptable when the currents involved have particularly high frequencies.